Lubricating oils



United States 2,836,561 LUBRICATING OILS John Scotchford Elliott andEric Descarnp Edwards, London, England, assignors to C. C. Wakefield &Company Limited, London, England, a British company No Drawing.Application May 9, 1955 Serial No. 507,147 Claims priority, applicationGreat Britain May 17, 1954 7 Claims. (Cl. 252-316) This invention is forimprovements in or relating to lubricating oils, and has particularreference to lubricating oils having extreme pressure properties, and tocutting oils and metal working oils.

A large number of organic compounds have been pro posed for use asextreme pressure agents, including various types of organic diandpolysulphides, and the corresponding derivatives of selenium. While thehigher polysulphides are very effective in increasing the film rupturestrength of the oil in which they are dissolved, they tend to beinherently unstable, corrosive, especially to copper and cuprousmaterials, and to exert a pro-oxidant effect upon the oil.

The potential corrosiveness of a sulphur-bearing organic compoundtowards cuprous metals is dependent both on the chemical structure ofthe compound and on the temperature at which it is employed. Thus, ingeneral, monosulphides are less corrosive than disulphides which, inturn, are less corrosive than the trior higher polysulphides; aromaticpolysulphides, in which the sulphur is directly linked to aromaticnuclei, are less corrosive than the corresponding aliphatic compounds,while the corrosiveness of any particular sulphide group can beappreciably influenced by the presence of other neighbouring groups.

Generally speaking the effectiveness of sulphur-bearing organiccompounds as extreme pressure additives for lubricating oils dependsupon the ease with which they reak down, yielding sulphur which thenreacts with the metal forming a sulphide film which prevents welding athigh loads. Thus, for example, the triand tetrasulphides will providereactive sulphur at lower temperatures than the correspondingdisulphides, and consequently are more effective extreme pressureadditives. Their corrosiveness to copper and cuprous metals, however, isa serious drawback, precluding their use in certain circumstances.

It is an object of the present invention to provide extreme pressurelubricants containing organic dior polysulphides, or their seleniumanalogues, which are normally corrosive to copper at 300 F. or below, inwhich the corrosiveness to copper or cuprous alloys is inhibited by theaddition of a novel combination of inhibitors.

It has already been proposed in United States patent specification No.2,414,257 to inhibit the copper staining tendencies of lubricantscontaining active sulphur by the addition of a minor proportion of amercapto-arylene thiazole or a derivative thereof, or an alkyl thiurammonoor disulphide.

We have now found that the staining of copper and cuprous metals bylubricants containing organic diand polysulphides orv their seleniumanalogues can be inhibited to an outstanding and unexpected degree bythe conjoint use of two additives of different types. These are: (a) acyclic compound containing the group 'i3-SH as part of a ring structureor a derivative thereof capable of homolytic dissociation into freeradicals aren't 0 N as part of a ring structure or a derivative thereofcapable of homolytic dissociation into free radicals t (LS N and (b) azinc, cadmium or iron salt of an organic dithiocarbamic acid.

More specifically additive (a) is a compound of general formula A-B inwhich A is a radical containing the group and B is a radical attached tothe sulphur atom, of such nature that the compound AB dissociateshomolytically at elevated temperatures yielding free radicals. Thus, Bmay be H, CH OH, -C(C H or it may be the same as A.

We have found that if B is a group, such as benzyl, butylaceto ordioctyl ammonium, which encourages heterolytic dissociation, thecompound is relatively ineffective as an inhibitor of copper staining.

A preferred sub-class of inhibitors of this type are 2-mercaptobenzothiazole B l G and its derivatives such as benzothiazoledisulphide, hydroxymethyl thiobenzothiazole and triphenyl methylthiobenzothiazole, but the corresponding derivatives of otherZ-mercaptothiazoles may be employed, for example, those having thegeneral formula where R and R may be the same or different and representhydrogen or hydrocarbon radicals, e. g., 2-mercapto-4-methyl-5-isopropyl thiazole. Examples of other types of additivecontaining the group l (J-SH as part of a ring structure are theZ-mercapto-oxazoles containing the group the Z-mercaptoimidazolescontaining the group the Z-rnercaptothiazines containing the group orisomers thereof and the Z-mercaptothiazolines.containing the group It isto be understood that the foregoing examples are merely illustrative ofthe more readily available types of compounds falling within category(a), and the invention is not intended to be restricted to these types.Itis also to be understood that derivatives of these mercapto com-,pounds may be employed, which dissociate homolytically yielding freeradicals, e. g., the disulphides.

'e. g., 2-mercapto-4-methyl thiazole,Z-mercaptobenzoxazole andZ-mercaptobenzimidazole, have not. The latter two compounds, however,may be used in certain synthetic lubricants, e. g., di(2-ethyl hexyl)sebacate, if desired. Mineral oil-soluble compoundscontaining oxa zoleand imidazole rings can, however, be obtainedby choosing suitable'alkylor alkylated aromatic substituents. The most effective compounds appearto be those containing a benzo radical adjacent to, the heterocyclicnucleus.

Additive (b) is a metal salt of an organic 'dithiocarbamic acid havingthe general formula t /VNC-S M R2 7 z where R 'and R may be the same ordifferent and repre-' sent preferably hydrocarbon'radicals althougheither R or R may be H, or' may together form part of a ring structure,M is zinc, cadmium or iron, and x is the valency of M. a

Specific examples of additives of this type are:

Zinc diethyl dithiocarbarnate Zinc di-n-butyl'dithiocarbamate Zinc di(methyl cyclopentamethylene) dithiocarbamate Cadmium di n-butyldithiocarbamate Ferric di n-butyl dithiocar'bamate Zinc mono-octyldithiocarbamate Cadmium pentamethylene dithiocarbamate Whereas theinhibitors ofgroup (a) are in themselves effective inhibitors of copperstaining by active sul- .phur, the compounds of group (b) are of littleor no value otherwise be possible. furthermore, it has been found 1 fthat the more effective inhibit orsof group (a) when used aloneprotectthe metal from-sulphur attack by forming face. a

The extreme: pressure additives employed in the lubri- 4 on the surfacea'coarse yellowish-brown film of the copper complex which is capable ofbeing removed by rubbing with consequent loss in Weight of the metal. Bythe conjoint use of the two types of additive, howeven'it is oftenpossible to obtain a bright untarnished copper surcating compositions ofthe present invention contain the group Cs,..-se,,o l l\ where m is 0,1, 2,3 or 4 and n is 0, l, 2 or 3 the sum of m and n being not less than2 and not greater than 4, the carbon atoms being attached to othercarbon atoms or to hydrogen or halogen atoms. a

More specifically these compounds may be simple or ganic di, tri ortetrasulphides, di'or tri-selenides or sulphoselenides. They may bealiphatic, aromatic or alicyclic compounds which may be unsubstituted orsubstituted by e. g., halogen atoms, nitro groups, hydroxyl groups orester groups. Alternatively, they'may be cyclic compounds in which thesulphur and/0r selenium-containing groups form part 'of a ringstructure.

Alternatively, the extreme pressure additives may be complex compoundsor mixtures of compounds obtained, for example, by sulphurisinga widevariety of unsaturated organic compounds such as lard oil, sperm oil,oleine, tallow, 'wool fat or various terpene derivatives.

, The precise chemical structure of these compounds is not known withcertainty. It'is known,'however, that when one or less than onemolecular proportionof sulphur per olefinic linkage is employed insulphurising an unsaturated organic compound, the'product'is generallynon-corrosive towards copper at 300 F. or higher; it is believed that insuch. materials the sulphur is presentas mono-sulphide linkages. Whenhigher amounts of sulphur are used, however, products are obtainedhaving varying degrees of chemical activity towards copper, dependingupon the amount of sulphur used and tempertaure of sulphurizing; It isbelieved in these latter compounds diand polysulphide linkages existwhich may form bridges between the molecules or be present in cyclicstructures.

The amounts of the extreme pressure additives employed will depend uponthe purpose for which the oil is to be used. Any quantity from theminimum sufficient to impart a substantial increase in film rupturestrength up to about 10 percent maybe employed, but in general fromabout 0.5 percent to about 2.0 percent is contemplated, especially foruse in turbine oils.

Specific examples of the extreme pressure additives employed in thepresent invention are:

Dibenzyl disulphide Dibenzyl trisulphide V I Di(3carbomethoxy-4-hydroxyphenyl) polysulphides as described. in UnitedStates patent specification No.

, Sulphuri'zed sperm oil Di(n-butyl) dithiodiace tate Di(n-butyl)trithiodiacetate Di n-butyl tetrathiodiacetate Di n-butyldiselenodiacetate tetrathiacyclo-octane Halogenated derivatives of theforegoing may also be employed.

It will be understood that the present invention applies' I not only tolubricants containing a-dior polysulphide or.

selenium analogue as the sole extreme pressure additive,

but also to lubricants containingadditionally other addi tives known toconfer extreme pressure properties such as organic halogenated compoundsand organic phosphorus compounds. A large number of such compounds areknown to the art. V 1 7 In one application of the present invention anextreme U pressure lubricant for the lubrication of hypoid gearscomprises a mineral lubricating oil, an organic dior polysulphidecompound (or selenium analogue) of the type hereinbefore described, andan organic halogenated compound e. g., a chlorinated paraflin wax,together with the two additives of types (a) and (b) to inhibit stainingof copper and cuprous metals.

In another application of the invention a turbine oil having extremepressure properties comprises a mineral lubricating oil and an extremepressure additive of the type described in United States patentspecification No. 2,691,000 having the general formula:

where R is an alkyl, aryl or cycloalkyl radical, X is sulphur orselenium and n is 2, 3 or 4 when X is sulphur, and 2 or 3 when X isselenium, together with additives of types (a) and (b) hereinbeforedescribed, to inhibit staining of copper and cuprous metals. Mixedsulphoselenides conforming to the above general formula are includedwithin the scope of the invention.

While the present invention is particularly concerned with lubricatingcompositions having a mineral lubricating oil base, it is alsoapplicable to lubricants consisting wholly or predominantly of fattyoils, e. g., castor oil or rapeseed oil, and to synthetic lubricantssuch as dicarboxylic acid diesters, e. g., di(Z-ethyl hexyl) sebacate,and polyglycol ethers.

In carrying out the present invention, the organic dior polysulphideextreme pressure additive is present in sufiicient quantity to impartextreme pressure properties to the oil while the inhibitors may each bepresent in amounts ranging from about 0.01 to about 1.0 percent. Ingeneral the best results are obtained by the use of the two inhibitorsin approximately equal amounts.

The present invention also includes an additive for use in a lubricatingcomposition, containing as an extreme-pressure additive an organic diorpolysulphide or their selenium analogues, to inhibit the copper orcuprous metal staining properties of the extreme-pressure additive,which additive comprises a mixture of (a) a cyclic compound containingthe group N as part of a ring structure or a derivative thereof capableof homolytic dissociation into free radicals N and (b) a zinc, cadmiumor iron salt of an organic dithiocarbamic acid.

The following examples are illustrative of compositions prepared inaccordance with the present invention: EMMPLE I An extreme pressurehypoid rear axle lubricant, con forming to the Society of AutomotiveEngineers (S. A. E.)

classification grade 90, was prepared having the following approximatecomposition:

% conventionally refined Mid-Continent oil of viscosity about 700seconds Redwood at F.

15.91% solvent refined mineral oil of viscosity seconds Redwood at 140F.

8% chlorinated paraffin wax (approx. 40% chlorine) 0.5%di(3-carbomethoxy 4-hydroxyphenyl) polysulphides prepared as describedin Example 4 of United States patent specification No. 2,388,047

0.25% di(3-carbomethoxy-4-hydroxyphenyl) thioether 0.14%Z-mercaptobenzothiazole 0.20% zinc di-n-butyl dithiocarbarnate EXAMPLEII A synthetic lubricant having extreme pressure properties consistingof di(2ethyl hexyl) sebacate, having dissolved therein:

1.0% di( 3-carbomethoxy-4-hydroxyphenyl) disulphide (prepared asdescribed in Example 2 of United States patent specification No.2,388,047

0.1% benzothiazole disulphide 0.1% zinc diethyl dithiocarbamate EXAMPLEIII An extreme pressure turbine oil conforming to British Admiraltyspecification O. M. 100 was prepared, consisting of approximately:

75% of a mineral oil having a viscosity of about 170 seconds Redwood at140 F.

25% of a solvent refined mineral oil having a viscosity of about 65seconds Redwood at 140 F.

to which blend was added:

1.5% di-n-butyl trithiodiacetate 0.1% benzothiazole disulphide 0.1% zincdi-n-butyl dithiocarbamate 0.07% ethylene glycol mononaphthenate acidphthalate (ferrous metal corrosion inhibitor) 0.001% calcium petroleumsulphonate EXAMPLE IV A cutting oil was prepared consisting of:

40% conventionally refined naphthenic base oil of viscosity about 140seconds Redwood at 140 F.

45% mineral oil of viscosity about 50 seconds Redwood at 140 F.

10% sulphurised olein 5% chlorinated paraffin wax (approx. 40% chlorine)to which blend was added:

0.1 Z-mercaptobenzothiazole 0.1% zinc di-n-butyl dithiocarbamate Thesulphurised olein used in this example contained about 24% sulphur andWas prepared by heating olein with sulphur at a temperature of about 170to 200 C.

for a period of about 40 minutes and then heating the product withfurther sulphur at a slightly lower temperature, e. g. to C. I

Table 1 Percentage Appearance of copper strips after of inhibitor TestNo. Inhibitor ((1) Percent (b) (zinc di-n-butyl dithio- 3 hours 24 hourscarbamate) None None Smooth black. Black, much flaking of coppersulphide. do 0.2 .do Black, considerable flaking. Benzothiazoledisulphide 0.2 None Dullcopper.-. Dtrk glrlplwn, with surace .-..do 0.10.1 Bright copper- Light peacock stain.

Hydlroxymethylthiobenzothia- 0.2 None Light; brown. As No. 3.

zo e. 6 do 0.1 0.1 Light peacock Medium brown/peacock. 72-Mercapto-4,6,6 trimethyl-1,3,6 0.2 None Purple brown. Black,considerable flak- H thiazine. ing. 8 d0 D. 1 0.1 Light brown} Lightbrown with some peacock. dark patches.

7 Test results in this table illustrate the effect of adding zincdi-n-butyl dithiocarba'mate to a lubricating oil consisting of the samemineral oil blend as in Example 111, containing 1.5% di-n-butyltrithiodiacetate, to which various copperstain inhibitors of type (a)had been added.

The tests were carried out by immersing clean copper strips, polishedwith carborundum powder, in the oils contained in l" test-tubes. Thetest-tubes were placed in an oil bath which was maintained at thedesired temperature in an oven. The oils were heated at 100 C. for 24hours.

Table 2 Percentage Appearance of copper strips aiter of inhib- TestInhibitor ((1) Percent itor (b) 7 No. (zinc di-ubutyl 3 hours 24 hoursdithio' carbamate) 9 2-Mercapto-benzoxazole. 0. 2 None Patches 12fblack, brown and Smooth black.

' peacoc 10 .do 0.1 0. 1 Bright, brassy with a little Light peacock.

light peacock stain. 11 2-1vIercapto-benzimidazole 0. 2 None Brown withblack patches- AsNo. 9. 12 clo 0.1 0.1 As No. 10 As No.10.

In this table a typical synthetic lubricant, di(2-ethy-l hexyl) sebacatewas employed, containing 1.5% di-nbut only those of zinc, cadmium andiron proved to be effective.

Table 4 Percent of Percent of Appearance oi copper after Test Sulphur orselenium benzotln'azinc No. compound Percent zole dibutyl disul dithio-3 hours 24 hours phide carbamate 21 Dibenzyl trisulphi deuu 1. 5 NoneNone Black, flaky Black, much flaking. 22 do. 1. 5 0. 2 None Lightpeacock Do. 23 1. 5 None 0. 2 Smooth black- Do. 24 1. 5 0. 1 0. 1 Brightcopper- Smooth black. 25 1.0 None None Dark'brown Black, slightly flaky.

acetate.

1. 0 0. 2 None Greenish brown Dark brown, patchy. 1. 0 None 0. 2 PeacockDark peacock. 1. 0 0.1 0.1 Bright copper Bright copper with brownpatches. 29 4.7 dimethyl-4,7 di 1. 0 None None Very dark brown. Black,flaky.

(2dimethyl propyD- 1,2,5,6 tetrathia-cyclooctane. 30 1.0 0. 2 None Verylight peacock- Do. 31 1. 0 None 0. 2 Brown Do. 32 1. 0 0.1 Bright copperSmooth black.

butyl trithiodiacetate, the temperature being 100 C. as

before. a e

The results in Table 4 illustrate the variety of organic diandpolysulphides and their selenium analogues which Table 3 PercentageAppearance of copper after- 'lestv of ben- Inhibitor (1)) Percent No.zothiazole disulphide 3 hours 24 hours 1 None None Smoothblack Black,much flaking of copper sulphide. 3 0.2 -do Dull copper Dark brown withsurface film. 13 0.1 do. Light brown Dark brown, dull with small blackpatches. 14 0.1 Zigc dimethyl dithiocar- 0.1 Bright copper..- Brightcopper.

amate. 15 0.1 Zinc diethyl dlthiocarbam- 0.1 l0 Light brown with patch-7 mate. 1 es of bright copper. 16 V 0.1 Cadmium dibutyl dithio- 0.1.....(10 Almost bright copper.

carbamate. 17 0.1 Cadmium pentamethylene 0.1 do Brown/peacock.

dithiocarbamate. 18 0.1 Ferric dlbutyl dithiocar- 0.2 do Brightorange.

bamate. 19 0.1 Nickel dibutyl dithioear- 0.2 Dull copper Very dark brownwith bamate. surface film. 20 0.1 Piperidine cyclopentameth- 0.1Darkbrown,black Dark brown, blackllaky ylene dithiocarbamate. patches.patches. p

The results in Table -3 illustrate the efiect of adding may be inhibitedby the combination of additives of the various dithiocarbamates toarmineral oil blend as in 75 present invention. 7 r a The compounds weredissolved in the same mineral oil blend as used in Table 1, the testbeing of 24 hours duration at 100 C.

The compound used in tests 29 to 32 was prepared by treatingdiisobutylene (2 mols) in benzene solution with sulphur monochloride (1mol) and reacting the product with alcoholic sodium disulphide to yielda product containing about 30% sulphur, consisting principally of theabove compound.

3. The turbine oil of claim 1 in which said dithiocarbamate is cadmiumdi-n-butyl dithiocarbamate.

4. The turbine oil of claim 1 in which said dithiocarbamate is ferricdi-n-butyl dithiocarbamate.

5. A lubricating composition comprising a lubricant base selected fromthe group consisting of mineral lubricating oil and a dicarboxylic aciddiester lubricating oil and a minor proportion, sufficient to impartextremepressure properties to the lubricant, of a compound capa- T able5 Percent of Percent of Test N o. Sulphur compound Percent 2-mercapzincdibutyl Appearance of copper after tobenzodithiocar- 18 hours thiazolebamate 33 Di-tertiary butyl disulphide 2. None None Black, very flaky.34 do 2. 0 0.2 None Darl: hbrown-black flaky pa 0 cs. 35 do 2. 0 0. 1Orange with dull deposit. 36 Sulphurized sperm oil 5.0 None None Verydark brown, flaky. 5.0 0.2 None Do. 5. 0 None 0. 2 Do. 5. 0 0. 0.1Brown/peacock, slightly flaky.

Table sets out the results of further tests which were ble of releasingreactive sulphur selected from the group carried out in the same baseoil blend, but for 18 hours consisting of organic disulphides andpolysulphides, to-

at 275 Fv gether with from 0.01 to 1.0 percent of an organic com- Table6 Appearance of copper after- Test N 0. Oil Composition 3 hours 24 hours40 Composition of ExampleI Bright gold Golden.

41 Composition of Example I Peacock, with dark Brown/peacock withwithout the zinc di-n-butyl spots. black spots. dithiocarbamate.

42 Composition of Example IV... Bright copper with Darkpeacock-smoothwith dark spots. black 111 places.

43 Composition of Example IV Dark peacock Black, flaky.

without the zinc di-n-butyl dithiocarbamate, but with an extra 0.1% of2-mercapt0benzothiazole.

It will be understood that the foregoing tests are designed todemonstrate the superiority of the miXed additives of types (a) and (b)as compared with either type used alone. At higher temperatures, or inthe presence of more active sulphur compounds, it may be necessary touse more than the 0.1-0.2 percent of the additives quoted in the aboveexamples, provided that compounds are selected having adequatesolubility in the lubricating oil base. On the other hand, in othercircumstances, e. g., to inhibit staining of copper at room temperature,quite small amounts of inhibitors, below 0.1 percent, may be sufiicient.

We claim:

1. A turbine oil comprising mineral oil containing from 0.5 to 2.0percent of a compound selected from the group consisting of di(n-butyl)dithiodiacetate and di(nbutyl) trithiodiacetate, together with from 0.05to 0.2 percent of benzothiazole disulphide and from 0.05 to 0.2 percentof an organic dithiocarbamate selected from the group consisting ofzinc, cadmium and iron dithiocarbamates.

2. The turbine oil of claim 1 in which said dithiocarbamate is zincdi-n-butyl dithiocarbamate.

in which n is an integer from 2 to 4 inclusive.

7. The lubricating composition of claim 5 in which said derivative ofsaid organic compound is benzothiazole disulphide.

References Cited in the file of this patent UNITED STATES PATENTS2,211,798 Story et al Aug. 20, 1940 2,414,257 Evans et a1 Jan. 14, 19472,629,694 Woods et a1. Feb. 24, 1953 2,691,000 Elliott Oct. 5, 19542,713,558 Schmitz July 19, 1955

1. A TURBINE OIL COMPRISING MINERAL OIL CONTAINING FROM 0.5 TO 2.0PERCENT OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF DI(N-BUTYL)DITHIODIACETATE AND DI(N BUTYL) TRITHIODIACETATE, DISULPHIDE AND FROM0.05 TO 0.2 PERCENT OFBENZOTHIAZOLE DISULPHIDE AND FROM 0.05 TO 0.2PERCENT OF AN ORGANIC DITHIOCARBAMATE SELECTED FROM THE GROUP CONSISTINGOF ZINC, CADMIUM AND IRON DITHIOCARBAMATES.